Although carbon black is generally used as a reinforcing agent for rubber, carbon black is black in color as its name indicates, a rubber molded article thus basically becomes black in color, and carbon black is thus unsuitable for manufacturing a rubber molded article of a pale color, such as a white color, etc., or any color besides black.
In particular among rubber molded articles, a paper feeding roller is used by being incorporated, for example, in a laser printer or other image forming apparatus making use of electrophotography, ink-jet printer, or an automatic teller machine (ATM), etc., and therefore being black in color tends to be shunned to prevent soiling of paper due to a rubbing mark.
Although decreasing the blending proportion of carbon black may be considered to reduce the influence of the color of carbon black, in this case, there is a problem that the reinforcing effect becomes insufficient so as to cause degradation, in particular, of mechanical characteristics, for example, tensile characteristics, such as tensile strength, elongation at break, etc., strain resistance characteristics, such as compression set, tension set, etc., of a rubber molded article.
It is thus being examined that amorphous silica, which, as a white reinforcing agent, exhibits the highest reinforcing effect, be blended in place of carbon black or together with carbon black or another reinforcing agent or filler, etc., such as titanium oxide, etc.
Also, a paper feeding roller is, for example, required to be excellent in ozone resistance, weather resistance, etc., for use inside an image forming apparatus and is required to be excellent in weather resistance, heat-aging resistance, cold resistance, low temperature characteristics, etc., in order to exhibit stable performance in an ATM, etc., that is installed in various locations, and is thus frequently formed of an ethylene propylene diene rubber (EPDM), which is excellent in these characteristics.
However, when, in particular, amorphous silica is blended as a reinforcing agent in a system using EPDM as a rubber and a peroxide crosslinking agent as a crosslinking agent, another new problem arises in that the amorphous silica inhibits the crosslinking of the EPDM by the peroxide crosslinking agent so that crosslinking does not occur at all or crosslinking occurs insufficiently and consequently, a rubber molded article having the required mechanical characteristics cannot be obtained.